The present invention relates to a process for production of sulphuric acid by condensation of sulphuric acid vapours from a gas mixture containing 0.01-10 vol. % of H2SO4 vapour calculated under the assumption that SO3 is fully hydrated and 0-50 vol. % of water vapour.
Sulphuric acid is in many cases produced from gases containing H2SO4 vapour and water vapour by condensation in a cooling process. However, it is known that by cooling and condensation of sulphuric acid vapours in gases containing water vapour a sulphuric acid mist is formed, i.e. an aerosol of small droplets of sulphuric acid.
From European Patent No. 0 417 200 B1 and U.S. Pat. No. 5,108,731 a process is known for production of sulphuric acid, in which sulphuric acid vapours in gas mixtures containing 0.01-10% H2SO4 vapour and 0-50% water vapour are condensed in vertical, acid-resistant tubes cooled externally with air or gas. The presence of large amounts of acid mist in the gas after condensation is avoided according to this patent by keeping the temperature difference between the sulphuric-acid containing gas flowing in an upward direction and the gaseous coolant flowing in a downward direction within certain specified limits. Most of the sulphuric acid mist generated during condensation may then be captured in a high-velocity aerosol fibre filter placed in top of each of the tubes as described in the patent.
In European Patent No. 0 419 539 B1 and U.S. Pat. No. 5,198,206 it is shown how the amount of acid mist escaping from condensation of sulphuric acid vapours from a gas mixtures containing 0.01-10% H2SO4 vapour and 0-50% water vapour can be reduced to below 10-15 ppm H2SO4 by adding solid particles to the gas before entering the condensation tower. The particles act as condensation nuclei for the sulphuric acid vapours and supress spontaneous homogeneous nucleation of small sulphuric acid droplets which are not easily captured in filtering devices.
In the following, the expression “sulphuric acid tower” means a packed absorption tower as described in U.S. Pat. No. 4,348,373 or a tower containing tubes as described in European Patent No. 0 417 200 B1.